A conventional wheel hub seal has an inner annular member and an outer annular member fitted on the outer periphery of the inner annular member. A space is formed between the inner annular member and the outer annular member. A resilient barrier is provided in the space. One end of the resilient barrier is fixed to the outer annular member. Another end of the resilient barrier is resiliently pressed against the inner annular member. Thereby, when the outer annular member is rotated relative to the inner annular member, the outer annular member drives the resilient barrier to rub against the inner annular member at a high speed to create a boundary lubrication effect, thereby achieving the purpose of preventing oil leaks.
However, in order to allow the outer annular member to rotate relative to the inner annular member, the inner annular member and the outer annular member must be spaced a distance apart from each other. As a result, the external silt may intrude into the seal from the space to damage the seal. In view of this, a dust-proof structure is provided in the space. As an example, the space is provided with a rubber block or the like. But, it is still impossible to prevent the silt from entering the space. The rubber block suffers a lot of wear and tear to lose its function after the seal is used for a long time. Accordingly, the inventor of the present invention has devoted himself based on his many years of practical experiences to solve these problems.